Flooding Regime and Restoration of Riparian Ecosystem Integrity

University of New Mexico

Department of Biology

J.F. Schuetz, M.C. Molles, Jr., C.N. Dahm and C.S. Crawford

• Damming and diversion of the river

• Altered volume and timing of the Rio Grande’s flow

• Isolated riparian forest (bosque)

• Reduced cottonwood germination; aging forest

• Invasion by exotic plants

• Limited scientific data to assess the ecological benefits of managed flooding

Why are we studying the Middle Rio Grande riparian forest?

iii) nativedetritivores

iii) net N mineralization

i) variation in water table depth ii) soil moisture

Cottonwoods

Forest Floor

Soils/Vadose Zone

Schematic Subsystems H°/predictions For flooded vs. nonfloodedsites:

i) interstitial DO Alluvial Aquifer ii) conductivity (salinity)

leaf litterwoody debris

water table

i) leaf decompositionii) forest floor respiration

ii) root growth/biomassi) C:N & C:P in new leaf tissue

iv) flowering iii) litterfall, C:N in litterfall

v) defoliation

Subsystems Under Study and Hypotheses

Study Sites

Total leaf biomassNative, non-cottonwood leaf biomassWood falling from the canopy

Preliminary Results

Average Annual Leaf Biomass Collected as Litterfallbars represent standard errors; * denotes significant difference

Leaf

Bio

mas

s (g

/m2 /y

r)

0

100

200

300

400

500

600

2000 2001*

Nonflood SitesFlood Sites

2002

Native and Exotic Leaf Biomass Excluding Cottonwood Leaves

Leaf

Bio

mas

s (g

/m2 /y

r)

0

10

20

30

40

50

60

Native leaf biomass excluding cottonwoodsExotic leaf biomass

Flood Nonflood

2000Flood Nonflood

2001Flood Nonflood

2002

*

Average Annual Woody Biomass Collected as Litterfallbars represent standard errors; * denotes significant difference

Woo

dy B

iom

ass

(g/m

2/y

r)

0

200

400

600

800

1000

1200

1400

1600

2000 2001 2002

Nonflood SitesFlood Sites

Coarse woody debris

Coarse Woody Debris (>2cm diameter) January 2002 and 2003bars represnet standard errors; * denotes significant difference

Ave

rage

Bio

mas

s of

Coa

rse

Woo

dy D

ebris

(M

g/ha

)

0

2

4

6

8

10

12

14

16

Nonflood SitesFlood Sites

2002* 2003

Pitfall traps – collecting ground arthropods

Beetle Assemblages at Flood and Nonflood Sites 2002

Total beetles:54 29

June 2002

157

20

98

Total beetles:275 43

June 2002

4

10

29

Flood Sites May 2002

Flood Sites 2: 33 Flood Sites 2: 5 Flood Sites 2: 16

33

516

Nonflood SitesMay 2002

2

1

26

Forest floor litter storage

Forest Floor Litter Storage (January 2002 and 2003)bars represent standard errors

Ash

-fre

e D

ry W

eigh

t of L

itter

Sto

rage

(g/

m2)

0

200

400

600

800

1000

1200

1400

1600

1800

Nonflood SitesFlood Sites

2002 2003

Soil moisture throughout a depth of 1 meter

Soil Moisture at Nonflood Sites (2001)

2001

Apr May Jun Jul Aug Sep Oct Nov DecV

olum

etric

wat

er c

onte

nt (

mL/

g so

il)

0.12

0.16

0.20

0.24

0.28

0.32

0.36

Rio

Gra

nde

Sta

ge a

t Ber

nard

o (f

t)

1

2

3

4

5

6

MonsoonrainsFlood pulse

Soil Moisture at Flood Sites (2001)

2001

Apr May Jun Jul Aug Sep Oct Nov Dec

Vol

umet

ric w

ater

con

tent

(m

L/g

soil)

0.12

0.16

0.20

0.24

0.28

0.32

0.36

Rio

Gra

nde

Sta

ge a

t Ber

nard

o (f

t)

1

2

3

4

5

6

25 cm below ground40 cm below ground55 cm below ground70 cm below ground85 cm below ground100 cm below groundMODAYYR vs Stage 01

MonsoonrainsFlood pulse

Net nitrogen mineralization

Net Nitrogen Mineralizationbars represnet standard errors; * denotes significant difference

Oct 01 Feb 02 Jun 02 Oct 02

ug N

O3-

+ N

H4+

/g s

oil

0

10

20

30

40

Flood Sites Nonflood Sites

Date Soils Collected

*

*

Groundwater levels

Depth to Water Table 2001* denotes significant difference

Jan Mar May Jul Sep Nov

Dep

th to

Wat

er T

able

(cm

)

20

40

60

80

100

120

140

160

180

Nonflood Sites

Flood Sites *

2001

• Contribute to the knowledge base of the scientific community – river restoration worldwide

• Provide local natural resource managers and water policy-makers with information to make decisions on the use of managed floods – costs and benefits

• Part of a larger initiative on restoring the river and bosque: Corps of Engineers, Bureau of Reclamation, Fish and Wildlife Service; Bosque Ecological Monitoring Project (BEMP); classes at UNM

What do we do with our results?

AcknowledgementsAcknowledgements

Funding agency: National Science Foundation Grant DEB-9903973

Undergraduate assistance: Karyth Becenti, Nate Bohls, Sam Gray, Leslie Barker, Joseph O’Connell, Nick Johnson, Ben Zimmerman

Cooperating agencies and institutions:Middle Rio Grande Conservancy DistrictBosque del Apache National Wildlife RefugeCity of Albuquerque Open Space DivisionNew Mexico State Land OfficeRio Grande Nature CenterGrinnell CollegeThe Nature Conservancy

Questions/Comments

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